1. Field of the Invention
The present method relates to the drying of a sand mold using a vacuum.
2. Description of the Prior Art
Cores and molds used in metal casting consist of a mass of refractory aggregate bound together to form a shape used as a pattern for molten metal during the casting process. The aggregate is typically coated with a binding material and then formed into a shape using a pattern. The binding material is typically hardened to hold the aggregate in the desired shape so the core or mold can be removed from the pattern. The core or mold is then used in giving shape to molten metal so that the metal takes the shape of the original pattern when the metal cools. In common usage, the mold forms the outer surface of the casting and the cores are used to form interior passages in the casting.
Sand molds made with no-bake binders can be very large, up to several hundred pounds of sand. Sand molds are typically made in open pattern boxes with the pattern on the bottom of the pattern box. After metal casting, the sand molds should be discarded or thermally reclaimed. The use of protein binder to bind the sand allows for partial recycling of unburned sand and binder. However, the procedure in the prior art patents disclosing the use of vacuum to dry sand molds does not work when the drying time is reduced to that of traditional binders because the vacuum level must be reduced thereby causing the sand molds to pop and crack severely.
Prior art includes patents on protein binder technology, including U.S. Pat. Nos. 5,320,157 and 5,582,231 to Siak et al. U.S. Pat. No. 5,320,157 discloses using a vacuum while a sand core is still at an elevated temperature after curing, such as about 70 to 80° C., to remove residual water from the core. A vacuum of at least about 101 Pascals, and more preferably from about 96.5 to 101 Pascals (0.72 to 0.76 Torr), for a duration of about 5 to 10 minutes is generally sufficient for this purpose. U.S. Pat. No. 5,582,231 discloses the use of standard core blowing equipment and air to dry the sand core. Traditional core machines with purge air have airflow from top to bottom, as indicated in the chapter on core making in ASM Handbook, Formerly Ninth Edition, Metals Handbook, Volume 15, Casting (1988).
The present invention allows for the use of a vacuum to dry sand molds made with no-bake binders which are hardened by solvent removal in a reduced amount of time without resulting in cracks or voids in the sand molds.